Quick answer
In a drawing, some text is language and some text is specification. Translating the second kind does not produce a bad translation — it produces a wrong part.
What must never be translated in a drawing
- Dimensions, tolerances, and units — a converted or reformatted number is a changed specification
- Standard designations and material codes (ISO, DIN, ANSI, GB references)
- Part numbers, drawing numbers, and revision marks
- Symbols for surface finish, welding, and geometric tolerancing
- Abbreviations that look like ordinary words but are defined terms in context
Why generic translation tools fail on drawings
- Drawings carry meaning through position: a note means something because of what it points at, and that link is lost when text is extracted
- Text is short and context-free, so a model has nothing to disambiguate from
- The language is bound to a technical standard, not to normal usage
- Vector line work and annotation layers are stored separately from the text
- A drawing exported as a scan has no text layer at all — see translating a scanned PDF
How to translate a drawing without changing it
- Freeze dimensions, units, symbols, and codes before translation begins
- Translate only explanatory text: notes, legends, title-block labels, revision descriptions
- Lock the terminology with a glossary so a term never varies between sheets
- Keep the source text visible alongside the translation so an engineer can verify rather than trust
- For drawing-specific handling, use the blueprint translator
Bottom line
Treat drawing translation as controlled technical work: decide what is frozen before you start, and have an engineer check the result against the original.